Angiotensin-converting enzymne (ACE) is a clinically important enzyme whose elevated circulating levels are associated with the pathogenesis of ?essential? hypertension, heart failure and renal failure. Consequently, inhibitors of this enzyme are widely used for clinical management of these diseases. ACE is a dipeptidyl carboxypeptidase whose natural substrates include the oligopeptides antiotensin I and bradykinin. It has two isozymes, sACE and gACE, which have simnilar enzymic activities. The two isozymes of ACE are expressed in a tissue-specific manner: gACE expression is restricted to developing male germ cells, whereas sACE is expressed in vascular endothelial cells, kidney tubular epithelial cells, intestinal brush border cells, monocytes and specific cell types in the brain. One of the major physiological functions of ACE that has been historically well recognized, is its role in blood pressure regulation through its participation in the renin-angiotensin system. However, recent results, most notably those arising from the ACE-knock-out mice, indicate a much broader spectrum of physiological roles of this enzyme. ACE-/- mice not only have lower blood pressure, but they also have abnormalities in kidney structure and function, and the male mice are sterile. In this application it is hypothesized that, although there is some redundancy, each physiological function of ACE is earned out by a specific isozyme expressed in a specific tissue. To test this hypothesis, transgenic ACE or its mutants will be expressed in ACE-/- mice using sperm-specific, vascular endothelial cell-specific and renal proximal tubular cell-specifictranscriptional promoters. Among the mutants to be tested are chimeric sACE-gACE, active site mutants and anchorless secreted mutants. These transgenic studies will be complemented with tissue-specific and temporally regulated ablation of expression of the ACE gene. The genetically modified experimental mice will be examined for male fertility, blood pressure, renal development and structural and functional defects of the kidney. These studies will clearly delineate the relationships between specific physiological functions of ACE and its expression in specific tissues. The proposed molecular approach using a combination of transgenic and conditional knock-out techniques will lead to a better understanding of the basis of multiple functions of ACE and may lead to the development of clinical protocols for blocking a specific function of ACE without inhibiting others.